When did they stop saying "please" and "thank you," start filling the entire overhead bin with their carry-on luggage and stop bathing?

The trendsetting airline industry, which has become the poster child for impoliteness in travel, wants you to believe it doesn't matter. It claims fares are low — an average $283 ticket price in 2012, which is roughly the same as 2001 after adjusting for inflation. It points to its almost-flawless safety record. Who cares that no one treats each other well?

But as 2013 draws to a close, you know something is wrong — very wrong — with the way we travel. Expedia's Airplane Etiquette Study, released last week, exposes the many ways we're annoyed. Topping the list: negligent parents, seat kickers and smelly seatmates.

Maybe it's up to the airline industry to revive our good manners next year. Maybe it's up to us, too.

Etiquette is on the decline everywhere. In survey after survey, travelers admit they forget to pack their manners when they hit the road.

"We've lost respect for each other," says Jacqueline Whitmore, author of the book Business Class: Etiquette Essentials for Success at Work. She should know. As a flight attendant for Northwest Airlines in the '90s, she had a front-row jump seat to the rise of rudeness in travel.

She and other experts believe that airlines are leading the way.

Some say the end of common courtesy coincides with the deregulation of the airline industry in 1978. Others claim it's the post-9/11 airline policies meant to prop up their sagging profits — edicts like "no waivers, no favors" that forced ticket agents to abide by an airline's rules, no matter how silly. But a lot of passengers think the final straw was unbundling, or removing amenities that traditionally were included with their ticket.

"Food, blankets and pillows used to be considered part of the deal when you fly," says Joy Martin, a retired postal worker from St. Louis. When airlines removed these extras or began charging for them, they made their cabins a less civil place.

It's difficult to say if travelers turned rude first, or if a demoralized workforce of overworked and underpaid flight attendants started this. Maybe it was a little bit of both. But we can all agree that the difference between "before" and "after" was dramatic.

David Miller, the president of a travel agency in Quebec, remembers a time not so long ago when "every airline employee welcomed you and treated you as a valued guest and client — better than they treat even first-class passengers today," he says. "Oh, for those good old times."

Remember, treating a customer with respect is free.

This is the perfect time to start thinking about reversing the trend, before the toxic effects of air travel seep deeper into the American hospitality industry, which used to be the envy of the world.

"We need to take a step back and think about our own behavior first," says Diane Gottsman, an etiquette expert who owns The Protocol School of Texas in San Antonio.

During the busy holiday travel season, do you give yourself enough time to get to the airport? If not, you'll stress out and may forget your manners, she says. Did you pack light? Nobody likes a bin hog. Are you considering the feelings of others? Yes, you on the armrest. And you, the guy leaning his seat all the way back into my knees.

Good manners make a great New Year's resolution for the airline industry, too. The domestic airline industry, which is on track to earn a handsome profit this year, needs to stop taking away from its passengers and start giving back. An occasional meal, a blanket, even a smile, might go a long way.

And as airlines go, so goes the rest of travel. Wouldn't it be great to travel with more class in 2014?

Christopher Elliott is a consumer advocate and editor at large for National Geographic Traveler. Contact him at chris@elliott.org or visit elliott.org.